Sorption And Separation of Various Materials By Graphene Oxides

ABSTRACT

Methods of sorption of various materials from an environment are disclosed herein. Embodiments of the materials include radioactive elements chlorates, perchlorates, organohalogens, and combinations thereof. Other embodiments pertain to methods of sorption of cationic radionuclides. Compositions produced by such methods are also disclosed herein. Embodiments of the methods may include contacting graphene oxides with the environment and sorption of the materials to the graphene oxides. In some embodiments, the sorption is relatively rapid in comparison to known sorbents; even in the presence of relatively higher concentrations of complexing agents. In some embodiments, the methods further include separating the graphene oxides that sorbed materials from the environment. Yet other embodiments may include desorbing the materials from the graphene oxides that sorbed the materials, and compositions therefrom.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. Utility patentapplication Ser. No. 14/001,255 entitled “Sorption and Separation ofVarious Materials By Graphene Oxides” filed on Nov. 26, 2013 whichclaims priority to International PCT Application Serial NumberPCT/US2012/026766 filed on Feb. 27, 2012 and having the same title asthe previously-mentioned co-pending application Ser. No. 14/001,255 andwhich claims priority to U.S. Provisional Patent Application Ser. No.61/446,535, filed on Feb. 25, 2011, The entirety of the above-identifiedapplications are each incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

This invention was made with government support under the U.S. Air ForceOffice of Scientific Research Grant No: FA9550-09-1-0581 and the U.S.Navy Office of Naval Research Grant No: N000014-09-1-1066, both awardedby the U.S. Department of Defense. The government has certain rights inthe invention.

BACKGROUND

Current methods of purifying various environmental contaminants(including radioactive elements and halogenated compounds) have numerouslimitations in terms of efficacy, costs, and efficiency. Therefore, aneed exists for the development of improved methods for purifying suchcontaminants from various environments.

BRIEF SUMMARY

In some embodiments, the present invention provides methods of sorptionof various materials from an environment. Such methods generally includecontacting graphene oxides with the environment. This in turn leads tothe relatively rapid rate or rates of sorption of the materials to thegraphene oxides. In some embodiments, rapid sorption of the materials tographene oxide occurs even in the presence of relatively highconcentrations of complexing agents. Complexing agents are agents thatmay compete with graphene oxide, or otherwise prevent or interfere withgraphene oxide sorbing materials from the environment. In someembodiments, the materials sorbed from the environment comprise at leastone of radioactive elements, chlorates, perchlorates, organohalogens,and combinations thereof. In some embodiments the complexing agents maybe one or more of Na⁺, Ca²⁺, NO₃ ⁻, CH₃COO⁻, C₂O₄ ²⁻, SO₄ ²⁻, Cl⁻, CO₃²⁻, and combinations thereof.

In some embodiments, the methods of the present invention also include astep of separating the graphene oxides from the environment after thesorption of the materials to the graphene oxides. In variousembodiments, the separation step may occur by centrifugation,ultra-centrifugation, filtration, ultra-filtration, precipitation,electrophoresis, reverse osmosis, sedimentation, incubation, treatmentwith acids, treatment with bases, treatment with chelating agents, andcombinations of such methods.

Various methods may also be used to contact graphene oxides with theenvironment. In some embodiments, the contacting occurs by mixing thegraphene oxides with the environment. In some embodiments, thecontacting occurs by flowing the environment through a structure thatcontains the graphene oxides (e.g., a column).

The sorption of materials to graphene oxides may also occur by variousmethods. In some embodiments, the sorption includes an absorptioninteraction of the materials in an environment to the graphene oxides.In some embodiments, the sorption includes an ionic interaction betweenthe materials in an environment and the graphene oxides. In someembodiments, the sorption includes an adsorption interaction between thematerials in an environment and the graphene oxides. In someembodiments, the sorption includes a physisorption interaction betweenthe materials in an environment and the graphene oxides. In someembodiments, the sorption includes a chemisorption interaction betweenthe materials in an environment and the graphene oxides. In someembodiments, the sorption includes a covalent bonding interactionbetween the materials in an environment and the graphene oxides. In someembodiments, the sorption includes a non-covalent bonding interactionbetween the materials in an environment and the graphene oxides. In someembodiments, the sorption includes a hydrogen bonding interactionbetween the materials in an environment and the graphene oxides. In someembodiments, the sorption includes a van der Waals interaction betweenthe materials in an environment and the graphene oxides. Theaforementioned interactions are non-limiting and herein referred to assorption.

Various graphene oxides may also be utilized in the methods of thepresent invention. For instance, the graphene oxides may be at least oneof functionalized graphene oxides, pristine graphene oxides, dopedgraphene oxides, reduced graphene oxides, functionalized graphene oxidenanoribbons, pristine graphene oxide nanoribbons, doped graphene oxidenanoribbons, reduced graphene oxide nanoribbons, stacked grapheneoxides, graphite oxides, and combinations thereof. In some embodiments,the graphene oxides may be functionalized with functional groups thatcomprise at least one of carboxyl groups, esters, amides, thiols,hydroxyl groups, carbonyl groups, aryl groups, epoxy groups, phenolgroups, phosphonic acids, amine groups, polymers and combinationsthereof. In some embodiments, the graphene oxides may be functionalizedwith polymers, such as polyethylene glycols, polyvinyl alcohols,poly(ethylene imines), poly(acrylic acids), polyamines and combinationsthereof.

Furthermore, the methods of the present invention may be utilized topurify various materials from various environments. For instance, insome embodiments, the environment is an aqueous solution, such ascontaminated water. In some embodiments, the environment is anatmospheric environment, such as air. In some embodiments, theenvironment is a solution comprising nuclear fission products.

In some embodiments, the materials to be purified include radioactiveelements. In some embodiments, the radioactive elements comprise atleast one of metals, salts, metal salts, radionuclides, actinides,lanthanides, and combinations thereof. In more specific embodiments, theradioactive elements in the environment include radionuclides, such asthallium, iridium, fluorine, americium, neptunium, gadolinium, bismuth,uranium, thorium, plutonium, niobium, barium, cadmium, cobalt, europium,manganese, sodium, zinc, technetium, strontium, carbon, polonium,cesium, potassium, radium, lead, actinides, lanthanides and combinationsthereof. In some embodiments, the radionuclide is actinide.

In some embodiments, the materials to be purified include chlorates,such as ammonium chlorate, barium chlorate, cesium chlorate, fluorinechlorate, lithium chlorate, magnesium chlorate, potassium chlorate,rubidium chlorate, silver chlorate, sodium chlorate, and combinationsthereof. In some embodiments, the materials to be purified includeperchlorates, such as ammonium perchlorate, barium perchlorate, cesiumperchlorate, fluorine perchlorate, lithium perchlorate, magnesiumperchlorate, perchloric acid, potassium perchlorate, rubidiumperchlorate, silver perchlorate, sodium perchlorate, and combinationsthereof. In additional embodiments, the materials to be purified includeorganohalogens, such as polychlorinated biphenyls (PCB) and halogenatedflame retardants.

In more specific embodiments, the methods of the present invention areused for the sorption of actinides from a solution comprising nuclearfission products. Such methods may also include a step of separating thegraphene oxides from the solution comprising nuclear fission productsafter the sorption step.

The methods of the present invention provide various advantages,including the effective separation of various radioactive elements fromvarious environments. For instance, in some embodiments, the methods ofthe present invention may be used to reduce radioactive elements in asolution by at least about 70%.

The methods of the present invention also provide various applications.For instance, in some embodiments, the methods of the present inventionmay be used for waste water treatment and environmental remediationapplications.

BRIEF DESCRIPTION OF THE FIGURES

FIGS. 1A-1C show data relating to the removal of various radionuclidesby graphene oxide. FIG. 1A shows the kinetics of U(VI), Am(III), Th(IV)and Pu(IV) sorption onto graphene oxide, indicating that steady stateconditions are reached within 5 minutes. FIG. 1B shows pH-sorption edgesfor Th(IV), U(VI), Pu(IV) and Am(III). FIG. 1C shows pH-sorption edgesfor Sr(II), Tc(VII), and Np(V) at steady state. With respect to the datashown in FIGS. 1A-1C, the concentrations are listed in Example 10.

FIG. 2A shows sorption isotherms for U(VI) in 0.01 M NaClO₄. FIG. 2Bshows sorption isotherms for Sr(II) in 0.01 M NaClO₄. FIG. 2C showssorption isotherms for Am(III) in 0.01 M NaClO₄. Isotherms were fittedwith both Langmuir (solid line) and Freundlich (dashed line) formalism.Parameters of fitting and sorption capacity (Q_(max)) are shown in Table1 (Example 3). The concentrations of the elements for sorption, and ofthe graphene oxides are listed in Example 10.

FIGS. 3A and 3B show sorption efficiencies of different materials thatare compared along with the coagulation properties of graphene oxidesolutions. FIG. 3A shows the removal of U(VI) from simulated liquidnuclear waste (see Table 2) by graphene oxide and also by some routinelyused sorbents at equal mass concentrations. FIG. 3B show the removal ofPu(IV) from simulated liquid nuclear waste (see Table 2) by grapheneoxide and also by some routinely used sorbents at equal massconcentrations. FIG. 3C shows coagulation of graphene oxide in asimulated nuclear waste solution. The left panel of FIG. 3C shows theinitial graphene oxide suspension (labeled as 1), and the coagulatedgraphene oxide (labeled as 2). The mid-right panel of FIG. 3C shows ascanning transmission electron microscope (STEM) image of the coagulatedgraphene oxide (labeled as 2) and the corresponding EDX spectrum on thefar right. The highlighted section in the STEM image in FIG. 3C showsthe formation of nanoparticulate aggregates containing cations fromsimulated nuclear waste solution (Si and P are trace contaminants ingraphene oxide from its preparation, as described in Example 5).

FIG. 4A shows micrographs and analyses of Pu/graphene oxide coagulates.The left side panel of FIG. 4A is a STEM image of Pu(IV) on grapheneoxide. The right side panels of FIG. 4A show the EDX spectracorresponding to the different areas labeled 1, 2 and 3 as indicated onthe STEM image. Pu-containing particles in graphene oxide could beobserved by Z contrast of the STEM image in FIG. 4A and as shown in theEDX spectra of the highlighted regions of the STEM image labeled 1, 2and 3. FIG. 4B is a high-resolution transmission electron microscopy(HRTEM) image of PuO_(2+x).nH₂O nanoparticles together with the FFT ofindividual nanoparticles from the highlighted region, indicating thecubic structure typical for PuO_(2+x).

DETAILED DESCRIPTION

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory only,and are not restrictive of the invention, as claimed. In thisapplication, the use of the singular includes the plural, the word “a”or “an” means “at least one”, and the use of “or” means “and/or”, unlessspecifically stated otherwise. Furthermore, the use of the term“including”, as well as other forms, such as “includes” and “included”,is not limiting. Also, terms such as “element” or “component” encompassboth elements or components comprising one unit and elements orcomponents that comprise more than one unit unless specifically statedotherwise. Ranges of values stated herein include all subranges and suchranges and subranges are included and disclosed herein.

The section headings used herein are for organizational purposes onlyand are not to be construed as limiting the subject matter described.All documents, or portions of documents, cited in this application,including, but not limited to, patents, patent applications, articles,books, and treatises, are hereby expressly incorporated herein byreference in their entirety for any purpose. In the event that one ormore of the incorporated literature and similar materials defines a termin a manner that contradicts the definition of that term in thisapplication, this application controls.

The nuclear industry generates large amounts of radioactive wastewaterthat must be effectively treated before it is discharged into theenvironment. The toxic radioactive elements (such as radionuclides) inthe wastewater cannot be effectively removed by current drinking waterpurification techniques. Furthermore, separation techniques involvingchromatographic methods can be time-consuming and expensive. Moreover,various industries generate large amounts of halogenated by-products,such as chlorates, perchlorates, and organohalogens (e.g.,polychlorinated biphenyls and halogenated flame retardants). As aresult, new methods are needed for the relatively rapid and efficientremoval of radioactive and halogenated elements from various solutionsand environments, especially for waste water treatment and environmentalremediation applications wherein relatively higher concentrations ofcomplexing agents may be present. The present invention addresses theseneeds.

In some embodiments, the present invention provides methods of sorptionof various materials from an environment. In some embodiments, thematerials to be removed from an environment include at least one ofradioactive elements, chlorates, perchlorates, organohalogens, andcombinations thereof.

Such methods generally include contacting graphene oxides with theenvironment. This in turn leads to the sorption of the materials to thegraphene oxides. In some embodiments, the methods of the presentinvention also include a step of separating the graphene oxides from theenvironment after the sorption of the radioactive elements to thegraphene oxides.

As set forth in more detail below, the methods of the present inventionhave numerous variations. For instance, the methods of the presentinvention may involve the purification of various materials from variousenvironments by the use of various graphene oxides.

Materials

The methods of the present invention may be utilized to purify variousmaterials from various environments. In some embodiments, the materialsto be purified include, without limitation, radioactive elements,chlorates, perchlorates, organohalogens, and combinations thereof. Inmore specific embodiments, the materials to be purified include, withoutlimitation, polycyclic aromatics, chlorinated and brominateddibenzodioxins and dibenzofurans, chlorinated biphenyls, lindane,dichlorodiphenyltrichloroethane (DDT) and other similar hydrophobicxenobiotics.

Radioactive Elements

In some embodiments, the radioactive elements to be purified from anenvironment are metals, salts, metal salts, radionuclides, actinides,lanthanides, and combinations thereof. In more specific embodiments, theradioactive elements in the solutions include radionuclides, such asthallium, iridium, fluorine, americium, neptunium, gadolinium, bismuth,uranium, thorium, plutonium, niobium, barium, cadmium, cobalt, europium,manganese, sodium, zinc, technetium, strontium, carbon, polonium,cesium, potassium, radium, lead, actinides, lanthanides and combinationsthereof.

In more specific embodiments, the radioactive elements to be purifiedfrom various environments include, without limitation, americium(III),actinide(III), actinide(IV), thallium(IV), plutonium(IV), neptunium(V),uranium(VI), strontium(II), technetium(VII), and combinations thereof.

In more specific embodiments, the radioactive elements include, withoutlimitation, thallium-201, iridium-192, fluorine-18, americium-241,americium-243, neptunium-237, Gd-153, niobium-93, barium-133,cadmium-109, cobalt-57, cobalt-60, europium-152, manganese-54,sodium-22, zinc-65, technetium-99, strontium-90, thallium-204,carbon-14, polonium 210, cesium-137, and combinations thereof.

In some embodiments, the radioactive elements may be naturally occurringradioactive materials (NORMs). In some embodiments, NORMs generallycomprise uranium and its isotopes. In some embodiments, NORMs may alsocomprise thorium and its isotopes. In further embodiments, NORMs mayalso include potassium, lead, and polonium. NORMs are not onlyconsidered in the context of their natural abundance and distribution,but also in view of human activities that increase potential forexposure to them. In some cases, those human activities may also serveto concentrate the radionuclides present, thereby resulting in what iscalled technologically enhanced naturally occurring radioactivematerials (TENORMs).

NORMs or TENORMs can be produced by oil and gas production and refining;mineral production; coal mining and combustion; metal mining andsmelting; fertilizer production; production of mineral based buildingmaterials, including granite, stone, gypsum, and concrete; andbeneficiation of mineral sands, including rare earth minerals, titaniumand zirconium. NORMs and TENORMs are also present in drinking watersupplies, particularly in Western US and Canada. See, e.g.,http://world-nuclear.org/info/inf30.html.

While uranium and thorium-based elements are the main isotopes of NORMsand TENORMs, K-40, Po-210, Ra-226, Ra-228, and Pb-210 can also bepresent. NORMs and TENORMs can also include actinides and lanthanides ingeneral. Thus, some embodiments of the present invention addresses theneed for the capture and clean-up of NORMs and TENORMs.

In more specific embodiments, the radioactive elements to be purifiedinclude actinides. In some embodiments, the actinides are in a solutionthat contains nuclear fission products.

Chlorates and Perchlorates

The methods of the present invention may also be utilized to purifyvarious chlorates and perchlorates. Non-limiting examples of chloratesinclude ammonium chlorate, barium chlorate, cesium chlorate, fluorinechlorate, lithium chlorate, magnesium chlorate, potassium chlorate,rubidium chlorate, silver chlorate, sodium chlorate, and combinationsthereof. Non-limiting examples of perchlorates include ammoniumperchlorate, barium perchlorate, cesium perchlorate, fluorineperchlorate, lithium perchlorate, magnesium perchlorate, perchloricacid, potassium perchlorate, rubidium perchlorate, silver perchlorate,sodium perchlorate, and combinations thereof. In some embodiments,perchlorates may have similar sorption profiles to various radioactiveelements, such as pertechnetate (Tc(VII)).

Organohalogens

The methods of the present invention may also be utilized to purifyvarious organohalogens. Organohalogens generally refer to organiccompounds that include one or more halogen groups. In some embodiments,the organohalogen is an organochloride. In some embodiments, theorganohalogen is polychlorinated biphenyl (PCB). In some embodiments,the organohalogen is a halogenated flame retardant. In furtherembodiments, the organohalogens include, without limitation,chloromethanes, dichloromethanes, trichloromethanes,tetrachloromethanes, bromomethanes, bromoalkanes, bromochloromethanes,iodoalkanes, iodomethanes, organofluorines, organochlorines, acyclicorganohalogens, cyclic organohalogens, and combinations thereof.

Environments

In the present invention, materials may be purified from various typesof environments. In some embodiments, the environment is an atmosphericenvironment, such as air. In some embodiments, the environment is asolution, such as an aqueous solution. Non-limiting examples of aqueoussolutions include water, such as radioactive water, contaminated water,and waste water. In some embodiments, the solution includes nuclearfission products. In some embodiments, the solution to be purified is anon-aqueous solution, such as a solution containing benzenes, toluenes,dichloromethane, and other non-aqueous solvents.

Graphene Oxides

“Functionalized graphene oxide,” as used herein, refers to, for example,graphene oxide that has been derivatized with a plurality of functionalgroups. “Chemically converted graphene” refers to, for example, grapheneproduced by reduction of graphene oxide. Reduction of graphene oxide tochemically converted graphene removes at least a portion of the oxygenfunctionalities present in graphene oxide.

Various graphene oxides may be utilized in the methods of the presentinvention. Suitable graphene oxides include, without limitation,functionalized graphene oxides, pristine graphene oxides, doped grapheneoxides, reduced graphene oxides, chemically converted graphene,functionalized graphene oxide nanoribbons, pristine graphene oxidenanoribbons, doped graphene oxide nanoribbons, reduced graphene oxidenanoribbons, stacked graphene oxides, graphite oxides, and combinationsthereof.

In some embodiments, the graphene oxides may be covalently ornon-covalently functionalized with various functional groups, such ascarboxyl groups, hydroxyl groups. carbonyl groups, aryl groups, epoxygroups, phenol groups, phosphonic acids (e.g., RPO(OH)₂, where R is acarbon group linked to the graphene scaffold), amine groups, esters,ether-based functional groups, polymers and combinations thereof.

In some embodiments, functionalized graphene oxides may be made fromgraphene oxide that has been derivatized with a plurality of functionalgroups using a derivitazing agent. In some embodiments, the derivatizingagent is a diazonium species. In some embodiments, the derivatizingagent is an aryl diazonium species. In some embodiments, the diazoniumspecies may be a pre-formed diazonium salt. In other embodiments, thediazonium species may be a diazonium salt that is formed in situ. Adiazonium species may be formed in situ, for example, by treating anamine with an organic nitrite such as, for example, isoamyl nitrite.

In some embodiments of functionalized graphene oxide, carboxylic acids,hydroxyl groups, carbonyl groups, and epoxides comprising the grapheneoxides (see, e.g., Table 3) may be chemically transformed by thederivatizing agents in forming the functionalized graphene oxide. Insome embodiments, functionalized graphene oxides generally contain aplurality of functional groups attached to the graphene oxide through acovalent bond. Chemical bonding of the functional groups may occur tothe edge of the graphene oxide, to the basal plane of the grapheneoxide, or to both the edge and the basal plane of the graphene oxide.

In some embodiments, the graphene oxides may be functionalized withpolymers, such as polyethylene glycols, polyamines, polyesters,polyvinyl alcohols, poly(ethylene imines), poly(acrylic acids), andcombinations thereof. Examples of suitable polyethylene glycolfunctional groups include, without limitation, triethylene glycoldi(p-toluenesulfonate), polyethylene glycol methyl ether tosylate, andthe like. In some embodiments, polyethylene glycol functional groups ongraphene oxides can be further hydrolyzed to remove most or all of anytosylate groups in order to afford terminal hydroxyl groups.

The graphene oxides of the present invention may also have variousarrangements. For instance, in various embodiments, the graphene oxidesof the present invention may be in stacked form. In some embodiments,the stacked graphene oxides may contain from about 2 layers to about 50layers of graphene oxide. In some embodiments, the graphene oxides ofthe present invention may form a single sheet.

In some embodiments, the graphene oxides of the present invention mayalso include one or more layers of graphene along with the grapheneoxides. Such graphenes may include, without limitation, pristinegraphenes, doped graphenes, chemically converted graphenes,functionalized graphenes and combinations thereof.

In further embodiments, the graphene oxides may be graphene oxidesderived from exfoliated graphite, graphene nanoflakes, or split carbonnanotubes (such as multi-walled carbon nanotubes). In more specificembodiments, the graphene oxides of the present invention may be derivedfrom split carbon nanotubes. In various embodiments, the split carbonnanotubes may be derived from single-walled carbon nanotubes,multi-walled carbon nanotubes, double-walled carbon nanotubes,ultrashort carbon nanotubes, pristine carbon nanotubes, functionalizedcarbon nanotubes, and combinations thereof. In more specificembodiments, the graphene oxides of the present invention are derivedfrom split multi-walled carbon nanotubes.

In addition, various methods may be used to split carbon nanotubes. Insome embodiments, carbon nanotubes may be split by potassium or sodiummetals. In some embodiments, the split carbon nanotubes may then befunctionalized by various functional groups, such as alkyl groups.Additional variations of such embodiments are described in U.S.Provisional Application No. 61/534,553 entitled “One Pot Synthesis ofFunctionalized Graphene Oxide and Polymer/Graphene OxideNanocomposites.” Also see Higginbotham et al., “Low-Defect GrapheneOxide Oxides from Multiwalled Carbon Nanotubes,” ACS Nano 2010, 4,2059-2069. Also see Applicants' co-pending U.S. patent application Ser.No. 12/544,057 entitled “Methods for Preparation of Graphene Oxides FromCarbon Nanotubes and Compositions, Thin Composites and Devices DerivedTherefrom.” Also see Kosynkin et al., “Highly Conductive Graphene Oxidesby Longitudinal Splitting of Carbon Nanotubes Using Potassium Vapor,”ACS Nano 2011, 5, 968-974.

In various embodiments, the graphene oxides may be doped with variousadditives. In some embodiments, the additives may be one or moreheteroatoms of B, N, O, Al, Au, P, Si or S.

In more specific embodiments, the doped additives may include, withoutlimitation, melamine, carboranes, aminoboranes, phosphines, aluminumhydroxides, silanes, polysilanes, polysiloxanes, sulfides, thiols, andcombinations thereof. In more specific embodiments, the graphene oxidesmay be HNO₃ doped and/or AuCl₃ doped.

In various embodiments, the graphene oxides of the present invention mayalso be dissolved or suspended in one or more solvents before beingcontacted with environments containing radioactive elements. Examples ofsuitable solvents include, without limitation, acetone, 2-butanone,dichlorobenzene, ortho-dichlorobenzene, chlorobenzene, chlorosulfonicacid, dimethyl formamide, N-methyl pyrrolidone, 1,2-dimethoxyethane,water, alcohol and combinations thereof.

In further embodiments, the graphene oxides of the present invention mayalso be associated with a surfactant before being associated withvarious environments. Suitable surfactants include, without limitation,sodium dodecyl sulfate (SDS), sodium dodecylbenzene sulfonate, TritonX-100, chlorosulfonic acid, and the like.

The graphene oxides of the present invention may have variousproperties. For instance, in some embodiments, the graphene oxides ofthe present invention have an aspect ratio in length-to-width greaterthan or equal to 2, greater than 10, or greater than 100. In someembodiments, the graphene oxides have an aspect ratio greater than 1000.In further embodiments, the graphene oxides of the present inventionhave an aspect ratio in length-to-width greater less than or equal to 2.

Furthermore, the graphene oxides of the present invention can come inthe form of variable sized sheets. Such sheets may have lengths ordiameters that range from about a few nanometers to a few hundredmicrons to several centimeters. In more specific embodiments, thegraphene oxides may have lengths or diameters that range from about 1nanometers to about 3 centimeters.

The graphene oxides of the present invention are generally hydrophilicand can be coagulated upon addition of cations or surfactants. In someembodiments, the graphene oxides have a ratio of total oxygenfunctionality to graphitic sp² carbon in the range of 2.6:1 and 4.0:1(for example, as in Table 3 further below Examples 6-7). All individualvalues and subranges within the range of 2.6:1 and 4.0:1 are includedherein and disclosed herein.

In other embodiments, the surface oxidation of the graphene oxides canbe gradually and systematically reduced to modify their properties. Suchreduction can occur through the addition of reducing agents (e.g.,hydrazine, sodium borohydride, acid or base with heat) or thermolysis(with or without H₂ being present). In some embodiments, graphene oxidemay be reduced with at least one reducing agent to form chemicallyconverted graphene. In some embodiments, the at least one reducing agentfor forming chemically converted graphene from graphene oxide may be,for example, hydrazines, iodide, phosphines, phosphites, sulfides,sulfites, hydrosulfites, borohydrides, cyanoborohydrides, aluminumhydrides, boranes, hydroxylamine, diamine, dissolving metal reductions,hydrogen, and combinations thereof. In some embodiments, the at leastone reducing agent may be hydrogen. In some embodiments, the grapheneoxide may be first reduced with hydrazine or hydrazine hydrate andthereafter reduced with a second, more powerful reducing agent such as,for example, hydrogen. The second reduction may further restore the sp²structure of pristine graphene sheets over that obtained in the firstreduction. In various embodiments, reduction of the graphene oxide withhydrogen may involve annealing the graphene oxide in the presence ofhydrogen. In some embodiments, annealing may include an inert gas.

Hydrazine, for example, removes ketone and hydroxyl groups from grapheneoxide but leaves behind edge carboxylic acid groups in the chemicallyconverted graphene. The residual carboxylic acid groups may disrupt theπ-conjugated network of the graphene sheet and lower the conductivity ofthe chemically converted graphene relative to that ultimately obtainableby their removal. Hydrogen may be more efficient than hydrazine atremoving oxygen-containing functional groups from the graphene oxide,since this reagent removes even carboxylic acid groups in addition tocarbonyl and hydroxyl functionalities. In some embodiments, borane (BH₃)may be used to reduce the graphene oxide. Borane is particularlyeffective at reducing carboxylic acids to alcohols, and the alcohols canbe further removed with hydrogen and heat in a second reduction step. Insome embodiments, the chemically converted graphene may be furtherreacted with a derivatizing agent to form a functionalized, chemicallyconverted graphene.

The graphene oxides of the present invention may also have variousforms. For instance, in some embodiments, the graphene oxides of thepresent invention may be associated with various composites. In someembodiments, such composites may include organic materials, such assynthetic polymers, natural fibers, nonwoven materials, and the like. Insome embodiments, the graphene oxide composites may include inorganicmaterials, such as porous carbons, asbestos, Celite, diatomaceous earth,and the like. In further embodiments, the graphene oxides of the presentinvention may be in isolated and pure forms.

In more specific embodiments of the present invention, the grapheneoxides are derived from the direct oxidation of graphite. In someembodiments, the oxidation of graphite could be through chemicalmethods, electrochemical methods or combinations of chemical methods andelectrochemical methods that may occur simultaneously or sequentially ineither order. In some embodiments, graphene oxides are derived by thechemical oxidation of graphite. Examples of methods of oxidizinggraphite are disclosed in Applicants' prior work. See, e.g., Marcano, etal., “Improved Synthesis of Graphene Oxide” ACS Nano 2010, 4, 4806-4814.Also see U.S. Provisional Patent Application Nos. 61/180,505 and61/185,640. Also see WO 20111016889, and corresponding U.S. PatentApplication Publication No. US 2012/0129736 published May 24, 2012.(Although stated elsewhere, each reference is hereby incorporated byreference in its entirety). In some embodiments, the graphene oxide mayhave a relatively higher level of oxidation, hydrophilicity and degreeof dispersability in relatively more polar solvents. In someembodiments, graphene oxides readily disperse in water.

In some embodiments, making graphene oxides may comprise providing agraphite source, providing a solution containing at least one acidsolvent, at least one oxidant (oxidizing agent) and at least oneprotecting agent, mixing the graphite source with the solution, andoxidizing the graphite source with the at least one oxidant (oxidizingagent) in the presence of the at least one protecting agent to formgraphene oxide.

In some embodiments of making the graphene oxides, and without beingbound by theory or mechanism, addition of what may be conceptuallythought of as a protecting agent operable for protecting alcohols ordiols may be included in the reaction mixture. In some embodiments ofmaking graphene oxides, such a protecting agent would be, for example,phosphoric acid. Phosphoric acid may be included in the reaction mixtureto prepare graphene oxides as provided in Examples 5-6, and Example 8.As demonstrated in those examples, regardless of the mechanism or mannerof protection, excessive basal plane oxidation in the graphene sheets isprecluded, while the overall level of oxidation is increased relative tothat of other methods for forming graphene oxide from bulk graphite.See, e.g., Table 3 and compare Examples 6 and 8 with Example 7.

In various embodiments, the at least one oxidant may be an oxidant suchas, for example, permanganate, ferrate, osmate, ruthenate, chlorate,chlorite, nitrate, osmium tetroxide, ruthenium tetroxide, lead dioxide,and combinations thereof. For any of the referenced oxidants that arecations or anions, any counteranion suitable for forming a salt of theoxidant cation or anion may be used in practicing the methods of thepresent disclosure. However, one of ordinary skill in the art willrecognize that certain salts may be more advantageous than others insuch properties as, for example, their solubility and stability. In someembodiments, the at least one oxidant is potassium permanganate. Ingeneral, the at least one oxidant of the present disclosure is anoxidant that mediates a cis-oxidation of double bonds.

In some embodiments, making the graphene oxides may further include atleast one acid solvent. The at least one acid solvent may be, forexample, oleum (fuming sulfuric acid), sulfuric acid, chlorosulfonicacid, fluorosulfonic acid, trifluoromethanesulfonic acid, andcombinations thereof. In some embodiments, the at least one acid solventmay be sulfuric acid. In some embodiments, the at least one acid solventis sulfuric acid and the at least one oxidant is potassium permanganate.In various embodiments, oleum may have a free sulfur trioxideconcentration ranging from about 0.1% to about 20%. In variousembodiments, sulfuric acid may have a concentration greater than about90% (v/v). Although Examples 5-8 employ potassium permanganate as the atleast one oxidant and sulfuric acid as the at least one acid solvent,one of ordinary skill in the art will recognize that many differentcombinations of oxidants, acid solvents and protecting agents may beused to achieve a similar result in preparing graphene oxides inpreparing graphene oxide while operating within the spirit and scope ofthe present disclosure.

In various embodiments, without meaning to be bound by any particulartheory or mechanism, the at least one protecting agent of the presentmethod is operable for protecting vicinal diols. In some embodiments,the at least one protecting agent is operable for protecting vicinaldiols in the presence of at least one acid solvent.

In some embodiments and without intending to be bound by any theory ormechanism, the at least one protecting agent is a non-oxidizing acid. Insome embodiments, the at least one protecting agent is an anhydride ormixed anhydride that is convertible to a non-oxidizing acid operable forserving as a protecting agent. Such protecting agents are operable forprotecting vicinal diols in the presence of a strong acid solvent suchas, for example, fuming sulfuric acid, sulfuric acid, chlorosulfonicacid, fluorosulfonic acid and trifluoromethanesulfonic acid.Illustrative protecting agents useful in any of the various embodimentsof the present disclosure include, for example, trifluoroacetic acid,phosphoric acid, orthophosphoric acid; metaphosphoric acid;polyphosphoric acid, boric acid, trifluoroacetic anhydride; phosphoricanhydride, orthophosphoric anhydride; metaphosphoric anhydride,polyphosphoric anhydride; boric anhydride; mixed anhydrides oftrifluoroacetic acid, phosphoric acid, orthophosphoric acid,metaphosphoric acid, polyphosphoric acid, and boric acid; andcombinations thereof. In some embodiments, the at least one protectingagent may be, for example, phosphoric acid, boric acid, trifluoroaceticacid, and combinations thereof. Although Example 5-6 and Example 8 eachutilize phosphoric acid as an illustrative protecting agent, similarresults have been obtained using trifluoroacetic acid and boric acid asthe protecting agent. In some embodiments, a salt of any of theaforesaid protecting agents may be used in the various methods presentedherein.

In various embodiments, oxidizing the graphite source takes place at atemperature between about −50° C. and about 200° C. In some embodiments,oxidizing takes place at a temperature between about 0° C. and about100° C. In some embodiments, oxidizing takes place at a temperaturebetween about 300° C. and about 85° C. In some embodiments, oxidizingtakes place at a temperature between about 30° C. and about 50° C. Insome embodiments, oxidizing takes place at a temperature between about25° C. and about 70° C. In some embodiments, oxidizing takes place at atemperature of less than about 50° C. In some embodiments, oxidizingtakes place at a temperature of less than about 30° C.

In general, reaction times may vary as a function of the reactiontemperature and as a function of the particle size of the startinggraphite source. In various embodiments, reaction times may vary fromabout 1 hour to about 200 hours. In other embodiments, reaction timesmay vary from about 1 hour to about 24 hours. In other embodiments,reaction times may vary from about 1 hour to about 12 hours. In stillother embodiments, reaction times may vary from about 1 hour to about 6hours.

At the aforesaid temperatures, a high recovery of graphene oxide havinga flake dimension approximating that of the starting graphite flakes andonly a small amount of mellitic acid and other low molecular weightbyproducts are observed. Operation at these temperatures is advantageousto minimize decomposition of the oxidant, particularly when the oxidantis KMnO₄. In strongly acidic media, permanganate slowly decomposes toMn(IV) species that are incapable of oxidizing graphite to grapheneoxide. Hence, the temperature is kept as low as possible to provide foressentially complete conversion of graphite to graphene oxide at anacceptable rate using only a moderate excess of KMnO₄. In thetheoretical limit of infinite size graphite crystals, for each gram ofgraphite being oxidized, 4.40 grams of KMnO₄ are required forstoichiometric equivalence. Losses of KMnO₄ to decomposition, formationof carboxylic acid groups and other basal plane edge functionality, andhole formation in the basal plane make the addition of oxidant somewhatabove the theoretical amount desirable.

In some embodiments of making graphene oxides, about 0.01 to about 10grams of KMnO₄ per gram of graphite (0.002 to about 2.3 equiv. KMnO₄)may be used.

In embodiments having sub-stoichiometric quantities of KMnO₄ or anyother oxidant, a co-oxidant may also be included to re-oxidize theprimary oxidant and make the reaction proceed to completion.Illustrative co-oxidants include, for example, oxygen andN-methylmorpholine N-oxide (NMO). In some embodiments of the presentdisclosure, about 6 grams of KMnO₄ per gram of graphite (1.4 equiv.KMnO₄) may be us to obtain graphene oxide having properties that aredifferent than previously known forms of graphene oxide.

In other various embodiments, methods of making graphene oxides includeproviding a graphite source, providing a solution containing at leastone acid solvent, at least one oxidant and at least one protectingagent, mixing the graphite source with the solution, and oxidizing thegraphite source with the at least one oxidant in the presence of the atleast one protecting agent to form graphene oxide. The at least oneprotecting agent is operable for protecting vicinal diols.

In still other various embodiments, methods of making graphene oxideinclude providing a graphite source, providing a solution containing atleast one acid solvent, potassium permanganate and at least oneprotecting agent, mixing the graphite source with the solution, andoxidizing the graphite source with the potassium permanganate in thepresence of the at least one protecting agent to form graphene oxide.The at least one acid solvent may be, for example, oleum, sulfuric acid,fluorosulfonic acid, trifluoromethanesulfonic acid, and combinationsthereof. The at least one protecting agent may be, for example,trifluoroacetic acid; phosphoric acid; or orthophosphoric acid,metaphosphoric acid; polyphosphoric acid; boric acid; trifluoroaceitcanhydride; phosphoric anhydride; orthophosphoric anhydride;metaphosphoric anhydride; polyphosphoric anhydride; boric anhydride;mixed anhydrides of trifluoroacetic acid, phosphoric acid,orthophosphoric acid, metaphosphoric acid, polyphosphoric acid, andboric acid; and combinations thereof.

In some embodiments of making graphene oxides, methods of the presentdisclosure further include isolating the graphene oxide. Isolating thegraphene oxide may take place by, for example, centrifugation orfiltration. In some embodiments, a poor solvent (e.g. ether) may beadded to a solution of graphene oxide to induce precipitation. In someembodiments, the methods further include washing the graphene oxideafter isolating the graphene oxide. For example, in some embodiments,the graphene oxide may be washed with solvents including hydrochloricacid, water, acetone, or alcohols to remove small molecule byproducts.In other embodiments, the graphene oxide may be washed with solutions ofbases. Washing with solutions of bases such as, for example, sodiumhydroxide, sodium carbonate or sodium bicarbonate afford the sodium saltof carboxylates or other acidic functional groups (e.g., hydroxylgroups) on the graphene oxide. Similarly, other basic salts of metalcations such as, for example, potassium, cesium, calcium, magnesium andbarium can be used.

Some embodiments of making graphene oxides may further include purifyinggraphene oxide. However, in alternate embodiments, the graphene oxidemay be used in an unpurified state. One of ordinary skill in the artwill recognize that various applications for the graphene oxide productmay require different levels of purity that might necessitate furtherpurification. Illustrative impurities that may remain in unpurifiedgraphene oxide include, for example, residual inorganic salts and lowmolecular weight organic compounds.

Contacting Graphene Oxides and Environments

Various methods may also be used to contact graphene oxides with variousenvironments that contain materials to be purified. In some embodiments,the contacting occurs by incubating the graphene oxides with theenvironment (e.g., an atmospheric environment). In some embodiments, thecontacting occurs by mixing the graphene oxides with the environment(e.g., an aqueous solution). The mixing may occur by conventionalmethods, such as agitation, sonication, and the like.

In some embodiments, the contacting of graphene oxides and anenvironment containing materials to be purified can also occur byflowing the environment through a structure that contains the grapheneoxides. In some embodiments, the structure may be a column or a sheetthat contains immobilized graphene oxides.

Additional methods of contacting graphene oxides with variousenvironments can also be envisioned. Generally, such contacting resultsin the sorption of radioactive elements in the environment to thegraphene oxides.

Sorption of Materials to Graphene Oxides

The sorption of materials to graphene oxides may also occur by variousmethods. In some embodiments, the sorption includes an absorption of thematerials in an environment to the graphene oxides. In some embodiments,the sorption includes an adsorption of the materials in an environmentto the graphene oxides. In some embodiments, the sorption includes anionic interaction between the materials in the environment and thegraphene oxides. In some embodiments, the sorption includes anadsorption interaction between the materials in an environment and thegraphene oxides. In some embodiments, the sorption includes aphysisorption interaction between the materials in an environment andthe graphene oxides. In some embodiments, the sorption includes achemisorption interaction between the materials in an environment andthe graphene oxides. In some embodiments, the sorption includes acovalent bonding interaction between the materials in an environment andthe graphene oxides. In some embodiments, the sorption includes anon-covalent bonding interaction between the materials in an environmentand the graphene oxides. In some embodiments, the sorption includes ahydrogen bonding interaction between the materials in an environment andthe graphene oxides. In some embodiments, the sorption includes a vander Waals interaction between the materials in an environment and thegraphene oxides. The aforementioned interactions are non-limiting andherein referred to as sorption.

The sorption of materials to graphene oxides may also have variouseffects. For instance, in some embodiments, the sorption leads to theformation of graphene oxide-cation colloids. In some embodiments, thesorption may lead to coagulation or precipitation.

Separation of Graphene Oxides from Environments

In some embodiments, the methods of the present invention also include astep of separating the graphene oxides from an environment containingvarious materials. The separation step generally occurs after thesorption of the materials to the graphene oxides. Various methods may beused for such separation steps. In some embodiments, the separation stepmay occur by centrifugation, ultra-centrifugation, filtration,ultra-filtration, precipitation, electrophoresis, sedimentation, reverseosmosis, treatment with acids, treatment with bases, treatment withchelating agents such as EDTA, and combinations of such methods.

In some embodiments, the separation step involves ultra-filtration. Inmore specific embodiments, the ultra-filtration step may lead to theremoval of formed graphene oxide-cation colloids from an environment. Inadditional embodiments, the graphene oxide-cation colloids may also beremoved by ultra-filtration, high speed centrifugation, sedimentation,reverse osmosis, or other suitable separation procedures.

In some embodiments, the separation step involves precipitation. In someembodiments, the precipitation can be initiated by adding one or morepolymers to an environment. For instance, in some embodiments, cationicpolyelectrolytes, such as poly(ethylene imine), may be added to asolution. In some embodiments, the solution may contain grapheneoxide-cation coagulants that precipitate upon the addition of polymers.The precipitated coagulants may then be removed by filtration,centrifugation or other methods.

The separation step may have various effects. In some embodiments, theseparation step may lead to a reduction of the radioactive elements inthe environment by at least about 70%.

In some embodiments, the separated graphene oxides may then be processedfurther in order to dissociate the sorbed materials (such as radioactiveelements). For instance, in some embodiments, the materials may bedissociated from the graphene oxides by changing the pH or temperatureof a solution. The dissociated graphene oxides may then be reused.

Advantages and Applications

The methods of the present invention provide numerous applications. Forinstance, the methods of the present invention can be used as filters orsorbents for removal of radioactive elements and halogenated compoundsfrom various sources. The methods of the present invention can also beused for nuclear waste treatment, and remediation of contaminatedgroundwater. For instance, the methods of the present invention can beused as components of ultra-filtration and reverse osmosis technologiesin waste water treatment. The methods of the present invention may alsobe used to mitigate environmental radionuclide contamination. Themethods of the present invention may also be used to separate varioushuman-made radionuclides from aqueous solutions of various compositions.In some embodiments, graphene oxides may also be used as components ofreactive barriers at contaminated sites.

In some embodiments, the methods of the present invention can be usedfor the sorption and separation of actinides from nuclear fissionproducts. A classic method for this separation involves using the PUREXprocess. However, the PUREX process involves multiple extraction andpreferential solubility steps and valence adjustments. Thus, by usinggraphene oxides in accordance with the methods of the present invention,one could mitigate the need for subsequent valence adjustments,extraction into organic phase, valence return, back extraction to theaqueous phase, and sometimes oxalate conversion to oxides.

To the best of Applicants' understanding, graphene oxides were not usedpreviously for the sorption or separation of radioactive elements orhalogenated compounds. Furthermore, effective separation of actinidesfrom aqueous solutions and nuclear wastes containing strong complexingagents (such as in nuclear fission products) were not previouslyreported.

In addition, the use of graphene oxides to purify radioactive elementsand halogenated compounds from various environments provides variousadvantages. To begin with, graphene oxides are comprised oftwo-dimensional materials that consist of single atomic planes.Therefore, graphene oxides provide a high surface area and a lowspecific mass, especially when compared to other potential sorbents.This in turn provides graphene oxides with optimal sorption kinetics forradioactive elements.

In addition, graphene oxides are hydrophilic materials withoxygen-containing functionalities that form stable complexes with manyradioactive elements, including actinides and lanthanide cations. Theseattributes can help lead to rapid macroscopic aggregation andprecipitation of the formed complexes from various solutions, includingwater. This process can be further facilitated by the use of additionalagents, such as surfactants and polymers.

Moreover, graphene oxides can be readily produced in mass quantities.Furthermore, the sorbed radioactive elements and halogenated compoundsthat are appended to graphene oxides can be liberated from the grapheneoxides upon the lowering of the pH in the solution. This in turnprovides for reversible leaching and sorption of radioactive elements.

ADDITIONAL EMBODIMENTS

Reference will now be made to more specific embodiments of the presentdisclosure and experimental results that provide support for suchembodiments. However, Applicants note that the disclosure below is forexemplary purposes only and is not intended to limit the scope of theclaimed invention in any way.

The Examples below pertain to the use of graphene oxides for effectiveradionuclide removal. In particular, we show the efficacy of grapheneoxide for rapid removal of some of the most toxic and radioactivelylong-lived human-made radionuclides from contaminated water, even inacidic solutions (pH<2). The interaction of graphene oxides withcations, including Am(III), Th(IV), Pu(IV), Np(V), U(VI) and typicalfission products Sr(II) and Tc(VII) were studied, along with theirsorption kinetics. Cation/graphene oxide coagulation occurs with theformation of nanoparticle aggregates on the graphene oxide surface,facilitating their removal. Graphene oxide is far more effective inremoval of transuranium elements from simulated nuclear waste solutionsthan other routinely used sorbents such as bentonite clays, iron oxideand activated carbon. These results point toward a simple methodology tomollify the severity of nuclear waste contamination that has beenspawned by humankind, thereby leading to effective measures forenvironmental remediation.

Treatment of aqueous waste effluents and contaminated groundwatercontaining human-made radionuclides, among which the transuranicelements are the most toxic, is an essential task in the clean-up ofnuclear legacy sites. The recent accident that included radionucliderelease to the environment at the Fukushima Daiichi nuclear power plantin Japan and the contamination of the water used for cooling its reactorcores, underscores the need for effective treatment methods ofradionuclide-contaminated water. Such technologies should beinexpensive, swift, effective and environmentally friendly. Grapheneoxide has been known for more than a century, but has attractedattention in the last decade due to its conversion to graphene.

The colloidal properties of graphene oxide make it a promising materialin rheology and colloidal chemistry. The amphiphilic graphene oxideproduces stable suspensions when dispersed in liquids and showsexcellent sorption capacities. Previously, it was shown that grapheneoxide enables effective removal of Cu²⁺, arsenate, and organic solvents.As a result of oxygen functionalization, the graphene oxide surfacecontains epoxy, hydroxyl and carboxyl groups (see, e.g., Table 3) thatare responsible for interaction with cations and anions. In this work,the application of graphene oxide for the effective removal of a varietyof radionuclides from aqueous solutions is described. Kinetics ofsorption, pH sorption edges and sorption capacity were studied in thebatch sorption mode to illustrate the performance of graphene oxide insequestering radionuclides from solution. Examples 1-4 described belowemployed the graphene oxide of Example 5. Preparation of the grapheneoxide of Example 5, and also several other examples of graphene oxideand chemically converted graphene oxide follow thereafter.

Example 1. Kinetics of Radionuclide Removal

The kinetics of radionuclide removal by graphene oxide are presented inFIG. 1A, indicating that near steady state conditions were achievedwithin 5 minutes even at very low graphene oxide concentrations (<0.1g/L by carbon). Without being bound by theory, it is envisioned that thefast sorption kinetics are likely due to graphene oxide's highlyaccessible surface area and lack of internal surfaces that usuallycontribute to the slow kinetics of diffusion in cation-sorbentinteraction. This fast kinetics are of importance for practicalapplications of graphene oxide for removal of cationic impurities,including Th(IV), U(VI), Pu(IV) and Am(III).

Example 2. Radionuclide Removal as a Function of pH

FIGS. 1B and 1C show pH sorption edges for Sr(II), Tc(VII), Np(V),Th(IV), U(VI), Pu(IV) and Am(III). All of the radionuclides demonstratetypical S-shaped pH-edges for cations, except for Tc, which exists asthe pertechnetate anion, TcO₄ ⁻. This explains its sorption at low pHwhen the graphene oxide surface is protonated and positively charged.For Lewis “hard” cations such as the actinides Th(IV), Pu(IV) andAm(III), the sorption is high, even from acidic solutions with pH<2. Forthese cations, the sorption from neutral pH solutions was nearlyquantitative, a result that is indicative of the prospects of itsapplication in remediation of contaminated natural waters.

Example 3. Graphene Oxide's Radionuclide Sorption Capacities

Graphene oxide demonstrates high sorption capacity towards U(VI), Sr(II)and Am(III) cations, as determined from sorption isotherms shown in FIG.2. Even with a graphene oxide concentration of only 0.038 g/L, thesaturation limit is not reached. The values for sorption capacitypresented in FIG. 2 are calculated from experimental data using Langmuirformalism and Freundlich formalism. The experimental results aresummarized in Table 1.

TABLE 1 Parameters for sorption of U(VI), Sr(II) and Am(III) on grapheneoxide Langmuir formalism Freundlich formalism Q_(max,) μmol/g K_(L,)L/μmol R² K_(F,) mol^(n-1)L^(n)/g n R² U(VI), pH = 3.5 97 ± 19 0.046 ±0.014 0.98 0.004 ± 0.002 0.33 ± 0.04 0.95 U(VI), pH = 5 116 ± 5  0.035 ±0.064 0.97 0.078 ± 0.026 0.68 ± 0.03 0.99 Sr(II), pH = 6.5 272 ± 35 0.026 ± 0.007 0.95 0.034 ± 0.017 0.55 ± 0.05 0.96 Am(III), pH = 3.5 2 ±1 7.034 ± 3.125 0.97 0.05 ± 0.03 0.67 ± 0.05 0.99

The above-mentioned results were obtained, despite the fact that thegraphene oxide surface was far from saturation. While it is difficult todirectly compare the sorption performance of different sorbents towardsradionuclides since it is dependent on the precise experimentalconditions, the sorption capacity of graphene oxide is much higher thanthat of activated carbon, bentonite clay and Fe(III) oxide, but close tothe value determined for oxidized carbon nanotubes (CNTs).

However, sorption rates for oxidized CNTs are much slower than those ofgraphene oxide since much of the CNT surfaces are internal orinaccessible due to bundling, and the CNTs have been investigated foronly a limited number of radionuclides and never with a large host ofcompeting counterions (referred to as complexing agents herein).Moreover, CNT synthesis and subsequent oxidation is far more expensivethan synthesis of graphene oxide, the latter coming from the one-pottreatment of graphite, thereby rendering graphene oxide more suitablefor large-scale clean-up operations.

Example 4. Removal of Radionuclides from Simulated Nuclear Waste

The removal of radionuclides from waste solutions was tested usingsimulated liquid nuclear wastes that contains U and Pu salts togetherwith Na, Ca and various complexing substances such as carbonate,sulfate, acetate, and citrate that could potentially complicate sorptionof radionuclides. See Table 2 for the complete list. Among the commonlyused scavengers for cationic radionuclides (such as bentonite clays,granulated activated carbon and Fe(III) oxide), graphene oxidedemonstrates the highest sorption ability towards actinides that formstrong complexes in solutions with sulfate, citrate, carbonate andacetate. The comparison of the sorption of different sorbents towardsU(VI) and Pu(IV) are presented in FIGS. 3A-3B. Remarkably, even forPu(IV) that forms strong complexes with such complexing agents insolution, the sorption onto graphene oxide was as high as 80%.

TABLE 2 Composition of Simulated Nuclear Waste at pH 7.5 Concentration,M Na⁺ 1.500 Ca²⁺ 0.005 NO³⁻ 0.806 CH₃COO⁻ 0.339 C₂O₄ ²⁻ 0.159 SO₄ ²⁻0.014 Cl⁻ 0.010 CO₃ ²⁻ 0.005

Upon the interaction of simulated nuclear waste solution with grapheneoxide, coagulation occurred that resulted in visual changes of thesuspension (FIG. 3C). A scanning transmission electron microscope (STEM)image of the graphene oxide coagulate with cations and a correspondingenergy-dispersive X-ray (EDX) spectrum are presented in FIG. 3C. This isin agreement with the earlier observations that addition of such cationsresults in coagulation of graphene oxide. The most important observationfor application of graphene oxide for radionuclides removal is that,despite the presence of high concentrations of cations that couldcompete with Pu for sorption sites, the sorption of Pu remains high.Thus, it is envisioned that the coagulation of graphene oxide suspensionresulting from cations and radionuclides would enable the effectiveremoval of radionuclides by filtration, reverse osmosis orsedimentation.

The interaction of Pu(VI) with graphene oxide results in itsstabilization as Pu(IV) and formation of nanoparticulate PuO_(2+x).nH₂Oon the graphene oxide (FIG. 4A). Such stabilization could be explainedby much higher sorption affinity of Pu(IV) towards the surfaces comparedwith Pu(V). The high resolution transition electron micrograph (HRTEM)image and EDX show that Pu is concentrated in aggregates of crystallinenanoparticles with an average size of 2 nm (FIG. 4B). The crystalstructure of nanoparticles corresponds to cubic Fm3m lattice withd-spacing typical for PuO₂ as studied by FFT. The reduction to Pu(IV) isalso supported by solvent extraction after Pu-leaching from grapheneoxide at pH 0.7. Upon acid leaching (see Example 5), only ˜10% of Pu(IV)was desorbed from graphene oxide after 15 minutes, indicating thatPu(IV) nanoparticles are kinetically stable. This is in concert with theearlier published data that Pu(IV) is minimally leached from sorbentsand more kinetically stable than Pu(V) or Pu(VI).

The experimental data verifies the ability of graphene oxide toeffectively sorb most toxic radionuclides from various solutions.Graphene oxide is found to be much more effective compared withbentonite days, activated carbon and Fe(III) oxide in actinide removalfrom liquid nuclear wastes. Graphene oxide containing radionuclide couldbe easily coagulated and precipitated. The simplicity of industrialscale-up of graphene oxide, its high sorption capacity, and it abilityto coagulate with cations makes it a promising new material forresponsible radionuclide containment and removal.

Experimental Protocols Example 5: Synthesis of Graphene Oxide Used inExamples 1-4 Above

Graphene oxide Example 5 was prepared using the improved Hummer'smethod. Marcano et al., ACS Nano 2010. 4:4806-4814. Large-flake graphite(10.00 g, Sigma-Aldrich, CAS 7782-42-5, LOT 332461-2.5 KG, Batch#13802EH) was suspended in a 9:1 mixture of sulfuric and phosphoricacids (400 mL). Next, potassium permanganate (50.00 g, 0.3159 mol) wasadded in small portions over a period of 24 hours. After 5 days, thesuspension was quenched with ice (1 kg) and the residual permanganatewas reduced with H₂O₂ (30% aqueous, ˜3 mL) until the suspension becameyellow. The product was isolated by centrifugation at 319 g for 90minutes (Sorvall T1, ThermoFisher Scientific) and subsequently washedwith 10% HCl and water. The yellow-brown water suspension (190.0 g) wasisolated, corresponding to 10 g of dry product. Gravimetric analysis andXPS shows 81% mass fraction of carbon in the dry product.

Example 6: Synthesis of Graphene Oxide in the Presence of a ProtectingAgent

A 9:1 mixture of conc. H₂SO₄:H₃PO₄ (360:40 mL) was added to a mixture ofgraphite flakes (3.0 g, 1 wt. equiv) and KMNO₄ (18.0 g, 6 wt. equiv),producing a slight exotherm to 35-40° C. The reaction was then heated to50° C. and stirred for 12 h. The reaction was cooled to RT and poured onto ice (˜400 mL) along with 30% H₂O₂ (3 mL). For work up, the mixturewas sifted through a metal U.S. Standard testing sieve (W. S. Tyler, 300μm) and then filtered through polyester fiber (Carpenter Co.). Thefiltrate was centrifuged (4000 rpm for 4 h), and the supernatant wasdecanted away. The remaining solid material was then washed insuccession with 200 mL of water, 200 mL of 30% HCl, and twice with 200mL of ethanol. For each wash the mixture was sifted through the U.S.Standard testing sieve and then filtered through polyester fiber. Ineach case, the filtrate was centrifuged (4000 rpm for 4 h), and thesupernatant was decanted away. The material remaining after the multiplewash process was coagulated with 200 mL of ether, and the resultingsuspension was filtered over a PTFE membrane with a 0.45 μm pore size.The solid obtained on the filter was vacuum dried overnight at roomtemperature. The yield was 5.8 g of a solid having a color similar tothat of peanut butter.

The yield of hydrophobic, under-oxidized graphite oxide removed duringthe first passage through the U.S. Standard testing sieve was 0.7 g.Visual observation of the hydrophobic, under-oxidized graphite oxideshowed the amount of recovered solid was significantly less than thatobtained by Hummers' Method (Example 7 below) or a modification ofHummers' Method (Example 8, further below).

Example 7. Synthesis of Graphene Oxide Via Hummers' Method

Concentrated H₂SO₄ (69 mL) was added to a mixture of graphite flakes(3.0 g, 1 wt. equiv) and NaNO₃ (1.5 g, 0.5 wt equiv), and the mixturewas cooled to 0° C. KMNO₄ (9.0 g, 3 wt. equiv) was added slowly inportions to keep the reaction temperature below 20° C. The reaction waswarmed to 35° C. and stirred for 30 min., at which time water (138 mL)was added slowly, producing a large exotherm to 98° C. External heatingwas introduced to maintain the reaction temperature at 98° C. for 15min, and the reaction was cooled using a water bath for 10 min.Additional water (420 mL) and 30% H₂O₂ (3 mL) were then added, producinganother exotherm. After air cooling, the mixture was purified asdescribed for Example 6. The yield was 1.2 g of a black solid. The yieldof hydrophobic, under-oxidized graphite oxide removed during the firstpassage through the U.S. Standard testing sieve was 6.7 g.

Example 8: Synthesis of Graphene Oxide Via a Modification of Hummers'Method

Graphene oxide was also synthesized by a modification of Hummers' Methodby including additional KMNO₄ in the reaction mixture. ConcentratedH₂SO₄ (69 mL) was added to a mixture of graphite flakes (3.0 g, 1 wt.equiv) and NaNO₃ (1.5 g, 0.5 wt. equiv), and the mixture was cooledusing an ice bath to 0° C. KMnO₄ (9.0 g, 3 wt. equiv) was added slowlyin portions to keep the reaction temperature below 20° C. The reactionwas warmed to 35° C. and stirred for 7 h. Additional KMnO₄ (9.0 g, 3 wt.equiv) was added in one portion, and the reaction was stirred for 12 hat 35° C. The reaction mixture was cooled to room temperature and pouredon to ice (˜400 mL) along with 30% H₂O₂ (3 mL). The mixture was thenpurified as described for Example 6. The yield was 4.2 g of a blacksolid. The yield of hydrophobic, under-oxidized graphite oxide removedduring the first passage through the U.S. Standard testing sieve was 3.9g.

Solid State ¹³C NMR Analysis of Graphene Oxide Examples 6-8

Solid state ¹³C NMR spectra for the graphene oxides of Examples 6-8 wereobtained at 50.3 MHz, with 12 kHz magic angle spinning, a 90° ¹³C pulse,41 ms FID and 20 second relaxation delay. In the ¹³C NMR spectra,signals near 190 ppm were assigned to carboxylates, signals near 164 ppmwere collectively assigned to ketone, ester and lactol carbonyl groups,signals near 131 ppm were assigned to graphitic sp² carbons and signalsnear 101 ppm were assigned to sp³ carbons of lactols. The signals near70 ppm were assigned to alcohols, and the upfield shoulder of this peakwas assigned to epoxides. Integral ratios are summarized in Table 3below. Table 3 also contains calculated integral ratios foralcohol/epoxide:sp² graphitic carbon and total oxygen containingfunctionality: sp² graphitic carbon as a measure of the degree ofoxidation.

TABLE 3 Summary of Integral Ratios in Solid State 13C NMR Analysis ofExamples 6-8 Graphene Oxide sp³ Alcohol/ Total Oxygen Example GraphiticAlcohol/ Lactol Epoxide:Graphitic Functionality:Graphitic No. CarbonEpoxide Carboxylate Carbonyl sp³ sp2 Ratio sp² Ratio 6 20 67 4 4 5 3.4:14.0:1 7 32 59 3 2 4 1.8:1 2.1:1 8 28 63 3 2 4 2.3:1 2.6:1

Solid state ¹³C NMR indicated that the graphene oxide of Example 6 wasmore completely oxidized than that of either Example 7 or Example 8. Thesimplest measure of the degree of oxidation is the ratio of thealcohol/epoxide peak integration to that of the graphitic sp² carbons. Apristine graphene plane having no edge functionalization would have aratio of zero, since all carbons would be of the sp² type. Uponoxidation to form graphene oxide, the number of sp² carbons in thegraphene plane decreases and oxygen-containing functionalitiescorrespondingly increase to produce a non-zero ratio. Higher ratios aretherefore indicative of a greater degree of oxidation. As shown in Table3, the graphene oxide of Example 6 was more oxidized than that of eitherExample 7 or Example 8, as evidenced by its greateralcohol/epoxide:graphitic sp² carbon ratio and total oxygenfunctionality:graphitic sp² carbon ratio.

Example 9. Reduction of Graphene Oxide

In some cases, hydrazine hydrate reduction was followed by annealing at300° C. in H₂. In general, hydrazine hydrate reduction was conducted bydispersing 100 mg of the graphene oxide material in 100 ml of deionizedwater and stirring for 30 minutes. Thereafter, 1.00 ml of hydrazinehydrate was added. The mixture was then heated for 45 minutes at 95° C.using a water bath. A black solid precipitated from the reactionmixture. The product was isolated by filtration on a 20 μm PTFE filterand as washed thereafter three times each with deionized water andmethanol.

Example 10. Sorption Experiments Using the Graphene Oxides of Example 5

Sorption experiments using the graphene oxides of Example 5 were carriedout in plastic vials for which sorption onto the vial walls wasnegligible under the experimental conditions. In the sorptionexperiments, radionuclides nitrates were added to graphene oxidesuspension. Next, the pH was measured by a glass combined pH electrode(In Lab Expert Pro, Mettler Toledo) and adjusted by addition of smallamounts of dilute HClO₄ or NaOH. After equilibration, the graphene oxidesuspension was centrifuged at 40000 g for 20 minutes (Allegra 64R,Beckman Coulter) to separate radionuclides sorbed onto the grapheneoxide. The sorption was calculated from the difference between theinitial activity of the radionuclides and that measured afterequilibration. The initial total concentration of radionuclides in thekinetic experiments and pH-dependence tests was 2.15×10⁻⁷ M for²³³U(VI), 1.17×10⁻⁸ M for ²³⁹Pu(IV), 5.89×10⁻¹⁴ M for ²³⁴Th(IV),3.94×10⁻¹⁰ M for ²⁴¹Am(III), 3.94×10⁻¹⁰ M for ²³⁹Np(V), 3.94×10⁻¹⁰ M for⁹⁵Tc(VII) and 1.24×10⁻⁷ M for ⁹⁰Sr(II). The concentration of thegraphene oxide suspension was 0.077 g/L in 0.01 M NaClO₄. In all cases,the total concentration of cations was much less than the solubilitylimit, and the graphene oxide/radionuclide ratio corresponded to a veryhigh under-saturation of graphene oxide sorption sites.

To measure the sorption capacity of graphene oxide towards differentradionuclides, the sorption isotherms were obtained using 0.038 g/Lgraphene oxide suspension in 0.01 M NaClO₄. The concentration of thecations was varied at constant pH values.

To demonstrate the performance of graphene oxide compared with otherroutinely used sorbents for radionuclide removal, experiments wereconducted with simulated nuclear wastes containing high concentrationsof complexing agents. The concentrations of actinides was equal to8×10⁻⁸ M for ²³³U(VI) and 3×10⁻⁹ M for ²³⁹Pu(IV).

For HRTEM examination, the graphene oxide containing Pu samples wereprepared such that the Pu(VI) at a total concentration of 1.14×10⁻⁵ Mwas added to the graphene oxide suspensions having a concentration of0.28 g/L at pH 4.8. After 18 hours, 99% of Pu was sorbed onto thegraphene oxide. The precipitated material was deposited onto acarbon-coated TEM grid and analyzed using HRTEM (JEOL-2100F) at anaccelerating voltage of 200 kV. EDX analysis was performed with aJED-2300 analyzer. For Pu leaching tests, concentrated HClO₄ was addedto the suspensions to make them pH 0.7. After 15 minutes, theconcentration of Pu in solution was measured.

Without further elaboration, it is believed that one skilled in the artcan, using the description herein, utilize the present invention to itsfullest extent. The embodiments described herein are to be construed asillustrative and not as constraining the remainder of the disclosure inany way whatsoever. While the preferred embodiments have been shown anddescribed, many variations and modifications thereof can be made by oneskilled in the art without departing from the spirit and teachings ofthe invention. Accordingly, the scope of protection is not limited bythe description set out above, but is only limited by the claims,including all equivalents of the subject matter of the claims. Thedisclosures of all patents, patent applications and publications citedherein are hereby incorporated herein by reference, to the extent thatthey provide procedural or other details consistent with andsupplementary to those set forth herein.

1. A method of radionuclide sequestration comprising: contactingsubstantially hydrophilic graphene oxides with a solution comprising atotal initial concentration of one or more cationic radionuclides and atotal initial concentration of one or more complexing agents, andreducing the total initial concentration of the one or more cationicradionuclides in the solution by at least forty percent by sorption ofthe one or more cationic radionuclides to at least a portion of thesubstantially hydrophilic graphene oxides.
 2. The method of claim 1wherein the total initial concentration of the one or more cationicradionuclides is equal to or less than 2.15×10⁻⁷ M.
 3. The method ofclaim 1, wherein the solution comprises an aqueous solution.
 4. Themethod of claim 1, wherein the contacting comprises mixing thesubstantially hydrophilic graphene oxides with the solution.
 5. Themethod of claim 1, wherein the sorption comprises absorption.
 6. Themethod of claim 1, wherein the substantially hydrophilic graphene oxidesare selected from the group consisting of functionalized grapheneoxides, chemically converted graphene, pristine graphene oxides, dopedgraphene oxides, reduced graphene oxides, functionalized graphene oxidenanoribbons, pristine graphene oxide nanoribbons, doped graphene oxidenanoribbons, reduced graphene oxide nanoribbons, stacked grapheneoxides, graphite oxides, and combinations thereof.
 7. The method ofclaim 1, wherein the one or more cationic radionuclides is selected fromcations of the group consisting of thallium, iridium, fluorine,americium, neptunium, gadolinium, bismuth, uranium, thorium, plutonium,niobium, barium, cadmium, cobalt, europium, manganese, sodium, zinc,technetium, strontium, polonium, cesium, potassium, radium, lead,actinides, lanthanides and combinations thereof.
 8. The method of claim1, further comprising adjusting the pH of the solution such that thereduction of the total initial concentration of the one or more cationicradionuclides occurs in about twenty minutes or less after contactingthe substantially hydrophilic graphene oxides with the solution.
 9. Themethod of claim 1, wherein the total initial concentration of the one ormore complexing agents in the solution is in the range of 2.4×10⁴ timesand 2.6×10¹³ times the total initial concentration of the one or morecationic radionuclides.
 10. The method of claim 1, wherein the one ormore complexing agents is selected from the group consisting of Na⁺,Ca²⁺, NO₃ ⁻, CH₃COO⁻, C₂O₄ ²⁻, SO₄ ²⁻, Cl⁻, CO₃ ²⁻, and combinationsthereof.
 11. The method of claim 1, wherein the substantiallyhydrophilic graphene oxides have a ratio of total oxygen functionalityto graphitic sp² carbon in the range of 2.6:1 and 4.0:1.
 12. The methodof claim 1, further comprising separating the graphene oxides from thesolution.
 13. The method of claim 12, wherein the separating comprisesat least one of the following: centrifugation, ultra-centrifugation,filtration, ultra-filtration, precipitation, electrophoresis, reverseosmosis, sedimentation, incubation, treatment with acids, treatment withbases, treatment with chelating agents, and combinations thereof. 14.The method of claim 12, wherein the separating comprises precipitatingthe graphene oxides from the solution by the addition of a polymer tothe solution.
 15. The method of claim 1, wherein the one or morecationic radionuclides is a cationic actinide and the solution iscomprised of nuclear fission products.
 16. The method of claim 15,further comprising separating the graphene oxides from the solutionafter the sorption.
 17. A method of radionuclide sequestrationcomprising: contacting substantially hydrophilic graphene oxides with asolution comprising nuclear fission products comprised of actinides, andreducing the concentration of the actinides in the solution by sorptionof at least a portion of the actinides to the substantially hydrophilicgraphene oxides.
 18. A method of radionuclide sequestration comprising:contacting substantially hydrophilic graphene oxides with a solutioncomprising one or more cationic radionuclides having a total initialcationic radionuclide concentration of 2.15×10⁻⁷ M or less, the solutionis additionally comprised of one or more complexing agents selected fromthe group consisting of Na⁺, Ca²⁺, NO₃ ⁻, CH₃COO⁻, C₂O₄ ²⁻, Cl⁻, SO₄ ²⁻,Cl⁻, CO₃ ²⁻, and combinations thereof; and sorbing the one or morecationic radionuclides to at least a portion of the substantiallyhydrophilic graphene oxides.
 19. The method of claim 18, furthercomprising reducing the total initial concentration of the one morecationic radionuclides by at least forty percent in about twenty minutesor less after contacting the substantially hydrophilic graphene oxides.20. The method of claim 18, further comprising desorbing one or more ofthe radionuclides from the graphene oxides that sorbed the cationicradionuclides and separating the desorbed radionuclides from thegraphene oxides to produce radionuclide-desorbed graphene oxides. 21.The method of claim 20, further comprising repeating the method of claim20 at least once wherein the graphene oxides comprise theradionuclide-desorbed graphene oxides.
 22. A composition comprisingradionuclide-sorbed graphene oxides prepared by the process ofcontacting substantially hydrophilic graphene oxides with a solutioncomprising one or more cationic radionuclides and one or more complexingagents, sorbing at least forty percent of the total initialconcentration of the one or more cationic radionuclides to at least aportion of the substantially hydrophilic graphene oxides therebyproducing radionuclide-sorbed graphene oxides, separating theradionuclide-sorbed graphene oxides from the solution.
 23. Aradionuclide composition prepared by the process of contactingsubstantially hydrophilic graphene oxides with a solution comprising oneor more cationic radionuclides and one or more complexing agents,sorbing at least forty percent of the total initial concentration of theone or more cationic radionuclides to at least a portion of thesubstantially hydrophilic graphene oxides thereby producingradionuclide-sorbed graphene oxides, separating the radionuclide-sorbedgraphene oxides from the solution, and desorbing one or more of theradionuclides from the radionuclide-sorbed graphene oxides.